Project Summary/Abstract The long-term goals of this project are to translate novel findings in the field of immunology into early phase immunotherapy clinical trials for patients with leukemia. Allogeneic hematopoietic cell transplantation (HCT) is a standard treatment for high-risk or relapsed AML and is potentially curative. However, major barriers to success in older AML patients include 1) an inability to tolerate intensive conditioning, 2) disease relapse, 3) graft-versus-host disease (GVHD), and 4) the lack of a suitable donor in many cases. One key immune player in mediating the graft-versus-leukemia (GvL) effect that also potentially limits GVHD is the NK cell. We hypothesize that new findings in NK cell biology can be translated to the clinic to improve the effectiveness and tolerability of HCT in older AML patients. Recent clinical studies have reported that HCT from an MHC-haploidentical donor (haplo-HCT) with myeloablative conditioning regimens that incorporate post-HCT cyclophosphamide results in clinical outcomes that are comparable to HCT from matched unrelated donors. However, one major obstacle to treating AML patients with haplo-HCT is the large number of older patients that are only candidates for reduced-intensity conditioning (RIC), which results in lower treatment-related mortality, but at the cost of a much higher incidence of AML relapse, and thus far, poor long-term disease-free survival. To address this important hurdle in the field, we will augment HCT with same-donor memory-like NK cell adoptive immunotherapy during the immediate post-HCT period, to enhance GvL while potentially improving engraftment and minimizing GVHD. Reports have recently identified that NK cells exhibit ?memory-like? properties following combined cytokine pre-activation. We and others have established that human memory-like NK cells respond robustly after a second stimulation and have multiple anti-tumor properties. We have translated this into a cellular therapy for relapsed/refractory (rel/ref) AML patients, and have completed a phase 1 study. However, one drawback of this allogeneic NK cell therapy is its rejection by the recipient's recovering immune system after 2-3 weeks, providing a short ?window of opportunity? for these NK cells to eliminate AML. To address this limitation in the NK immunotherapy field, we will incorporate a donor-matched RIC HCT, providing an ideal immune-compatible environment for memory-like NK cells to expand and attack residual AML. In this proposal, we will 1) test the safety and efficacy of augmenting RIC HCT with same-donor memory- like NK cell adoptive immunotherapy in a phase 2 clinical trial for patients with AML, 2) define memory-like NK cell correlates of clinical response, and elucidate key mechanisms important for memory-like NK cell anti-AML responses. These studies will lead to a new understanding of mechanisms whereby NK cells effectively attack AML, and whereby AML resists NK cell therapy, and hence strategies to improve memory-like NK cell anti- AML responses in future clinical trials.